The water solubility index (WSI) is a parameter that indicates
the total degradation undergone by starch granules; that is, it is the
integration of the effects of gelatinization, dextrinization, and the
consequent solubilization of starch (Gutkoski & El-Dash, 1999).
Table 1 shows the effect of barrel temperature, feed rate, screwspeed, and moisture content on WAI. Increasing feed rate significantly
(p ¼ 0.002) increased WSI of bean extrudates. The average
WSI values for 80 and 120 g/min feed rate (FR-1 and FR-2) were
18.14 and 20.56, respectively. The increased WSI under high feed
rate was probably due to fully developed flow along the die which
also increases starch and/or fiber degradation during extrusion
cooking. Hashimoto and Grossman (2003) reported the similarWSI
results for extruded cassava bran/cassava starch blend.Extruded
product properties depend mostly on the molecular transformations,
for example, disruption of starch granules, depolymerization
of amylose and amylopectin; these transformations are
generated in the various parts of the extruder by pressure, shearing
and residence time